The invention relates to a method for increasing the efficiency of surfactants with concur-rent suppression of lamellar mesophases, particularly in microemulsions and emulsions, as well as to surfactants with an additive admixed thereto.
According to the state of the art, emulsions and microemulsions are stabilized by non-ionic, anionic or cationic surfactants. The surfactants are capable of solubilizing a non-polar solvent (oil) in a polar solvent (for example, water). The efficiency of the surfactants is expressed by the amount of surfactant that is needed to solubilize a certain portion of oil in water or vice versa. Moreover, in the case of water-oil-surfactant mixtures, a distinction is made between emulsions and microemulsions. Whereas microemulsions are thermodynamically stable, emulsions are thermodynamically unstable and they disintegrate. On the microscopic level, this difference is reflected by the fact that the emulsified liquids in microemulsions are expressed in terms of smaller liquid volumes (for instance, 10xe2x88x9215 xcexcL) than in emulsions (for instance, 10xe2x88x9212 xcexcL). Therefore, thermodynamically un-stable emulsions exhibit larger structures.
Lamellar mesophases can occur in microemulsion systems. Lamellar mesophases cause optical anisotropy and increased viscosity. These properties are undesirable, for example, in detergents, because the lamellar mesophases cannot be washed out. Moreover, additives generally influence the temperature behavior of emulsions and microemulsions. For instance, a shift of the monophase areas for oil-water-surfactant mixtures to other temperature ranges can be observed in the phase diagram when an additive is admixed. These shifts can be in the order of magnitude of 10xc2x0 C. [18xc2x0 F.]. This, however, makes it necessary, for example, to change the detergent formulations in order to adapt them to the new temperature behavior that prevails in the monophase area. In addition, while saving on surfactants, there is a need to achieve an emulsifying behavior that is at least as good and to reduce the interfacial surface tension, which translates into an improvement of the washing power of detergents, for example.
Consequently, the objective of the invention is to raise the efficiency of surfactants and to reduce even further the interfacial surface tension between water and oil in the presence of surfactants. Furthermore, the occurrence of lamellar phases in microemulsions or water-oil-surfactant mixtures is to be suppressed. The temperature behavior of the emulsions and microemulsions is to remain unaffected by the admixture of the additive, that is to say, the admixture of the additives should not have very much influence on the position of the monophase area in the phase diagram in terms of the temperature. An additive is to be created that does not impact upon the position of the monophase area in terms of the temperature. An additive is also to be created that has the above-mentioned advantages and that can be admixed, for example, to a detergent, without the need to change the formulation of the remaining detergent formulation. The possibility is to be created to prepare microemulsions in which the size of the emulsified liquid particles corresponds to that of emulsions.
Surprisingly, based on the generic part of claim 1, all of these objectives are achieved according to the invention in that a block copolymer having a water-soluble block A and a water-insoluble block B is used as the additive.
According to the invention, the addition of the AB block copolymer to the water-oil-surfactant mixture does not change the monophase area in the phase diagram in terms of the temperature; the efficiency of the surfactant mixture is considerably increased, lamellar mesophases are suppressed in microemulsions and the interfacial surface tension between water and oil is reduced to a greater extent than with the surfactants alone. Moreover, microemulsions retain their characteristic properties while their structure size is increased; for instance, the emulsified structures acquire sizes of up to approximately 2000 xc3x85. This gives rise to a microemulsion that has the structural sizes of an emulsion but that is thermodynamically stable. The size of the emulsified liquid particles depends on the temperature and on the amount of block copolymer added, and thus on the composition of the surfactant mixture.
Advantageous embodiments of the invention ensue from the subordinate claims.
Blocks A and B can have molecular weights between 500 u and 60,000 u. Preference is given to the use of a polyethylene oxide (PEO) block as block A However, it is possible to employ all blocks A that are water-soluble, so that, together with block B, they form an amphiphile. Other examples of block A are polyacrylic acid, polymethacrylic acid, poly-styrene sulfonic acid as well as their alkali-metal salts in which the acid function has been at least partially substituted by alkali-metal cations, polyvinyl pyridine and polyvinyl alcohol, polymethyl vinyl ether, polyvinyl pyrrolidine, polysaccharides as well as mixtures thereof.
Various water-insoluble components with the above-mentioned molecular weight can be used as block B. Thus, for instance, block B can be the product of an anionic 1,2-polymerization, 3,4-polymerization or 1,4-polymerization of dienes. Consequently, block B can also be the product of an at least partial hydration of polydienes. Examples of typically used monomeric components are 1,3-butadiene, isoprene, all of the constituents *) of dimethyl butadiene, 1,3-pentadiene, 2,4-hexadienes, xcex1-methyl styrene, isobutylene, ethylene, propylene, styrene or alkyl acrylates and alkyl methacrylates, whereby the alkyl group contains between 2 and 20 carbon atoms. Block B can also be polydimethyl siloxane. The polymer of a single monomer or of a monomer mixture can be employed as block B.
Translator""s note: the German original uses the word xe2x80x9cKonstitumerexe2x80x9d, which apparently does not exist since it is not to be found in reference works for the German language (the English xe2x80x9cequivalentxe2x80x9d would be xe2x80x9cconstitumersxe2x80x9d), but perhaps the author meant something along the lines of xe2x80x9cconstituentsxe2x80x9d. Block B can have methyl, ethyl, vinyl, phenyl or benzyl groups as side chains. 
The double bonds in the polydiene chain as well as in the vinyl groups, which can be pre-sent as a side chain, can be either totally or partially hydrated. According to the invention, however, any sufficiently amphiphilic block copolymer can be used. The AB block co-polymers used according to the invention are preferably obtained by means of anionic polymerization.
If blocks A and B have low molecular weights in the order of magnitude of about 500 to 5000 g/mol, particularly advantageous properties of the AB block copolymers according to the invention can be observed in the application products. For instance, the polymers with such low molecular weights dissolve rapidly and thoroughly. This is true, for example, of solutions in soaps and detergents.
In the AB block copolymers employed according to the invention, the two blocks A and B should have the largest possible difference in their polarity. In this context, block A should preferably be polar and block B preferably nonpolar. This increases the amphiphilic behavior. Block A should be water-soluble and block B should be soluble in non-polar media. Advantageously, block B should be soluble in mineral oils or aliphatic hydrocarbons or else soluble in mineral oils and aliphatic hydrocarbons. This also applies at room temperature.
Furthermore, it is also possible to employ AB block copolymers of the types ABA and BAB, which are designated as triblock copolymers.
For example, the following surfactants (C) and their mixtures can be used with the additives according to the invention:
non-ionic surfactants of the class of alkyl polyglycol ethers (CiEj) wherein ixe2x89xa78 (C=carbon atoms in the alkyl chain, E=ethylene oxide units);
non-ionic surfactants of the class of alkyl polyglucosides (APG) xe2x80x9csugar surfactantsxe2x80x9d, CiGj wherein ixe2x89xa78 with alcohol as a co-surfactant (CXxe2x80x94OH, xxe2x89xa76);
anionic surfactants, for example, AOT (sodium bis-(2-ethyl hexyl)-sulfosuccinate);
cationic surfactants
surfactant mixtures
industrial surfactants
A few terms and expressions will be explained below:
C=any desired surfactant, such as anionic, cationic, non-ionic surfactant or sugar surfactant as well as their mixtures containing at least two surfactants
D=additive that, according to the invention, is admixed to the surfactant C
xcex3=total surfactant concentration (weight fraction) consisting of C and D, wherein   γ  =                    m        ⁢                  xe2x80x83                ⁢                  (          C          )                    +              m        ⁢                  xe2x80x83                ⁢                  (          D          )                            m      total      
xe2x80x83wherein
m=weight in g
xcex3=dimensionless weight fraction
mtotal=weight consisting of mwater=motl+m(C)+m(D)
{overscore (xcex3)}=total surfactant concentration at the point of intersection at which the monophase area meets the tri-phase area in the phase diagram. At the given water-to-oil ratio, this corresponds at least to the total surfactant concentration needed for complete solubilization of water and oil
xcex4=weight fraction of additive D in the mixture consisting of surfactant C+additive D, corresponding to   δ  =            m      ⁢              xe2x80x83            ⁢              (        D        )                            m        ⁢                  xe2x80x83                ⁢                  (          C          )                    +              m        ⁢                  xe2x80x83                ⁢                  (          D          )                    
xe2x80x83wherein
m=weight in g and
xcex4=weight fraction (dimensionless)
The invention will be illustrated below with reference to an example. PX/Y=additive with a molecular weight in [sic] 1000 g/mol of X of*) a hydrophobic alkyl chain (hydrated 1,4-polyisoprene) and a molecular weight in 1000 g/mol of Y of polyethylene oxide.
Translator""s note: there seems to be something wrong with the prepositions used in this sentence in German, starting with xe2x80x9chaving a molecular weight in 1000 g/molxe2x80x9d instead of xe2x80x9chaving a molecular weight of 1000 g/molxe2x80x9d and then also in xe2x80x9c1000 g/mol of X of hydrophobic alkyl chainxe2x80x9d and in xe2x80x9c1000 g/mol of Y of polyethylene oxidexe2x80x9d (the German preposition used here could also be translated as xe2x80x9conxe2x80x9d, but although xe2x80x9c1000 g/mol of X on the hydrophobic allyl chainxe2x80x9d might be seen as okay, xe2x80x9cY on polyethylene oxidexe2x80x9d sounds odd). 
Example P5/5: the alkyl chain has a molecular weight of 5000 g/mol (=u) and the poly-ethylene oxide chain has a molecular weight of 5000 g/mol.
P22/15: the alkyl chain has a molecular weight of 22,000 g/mol and the polyethylene oxide chain has a molecular weight of 15,000 g/mol.
The additives thus prepared are AB block copolymers.
The compounds shown here as examples can be obtained employing the preparation method described in DE 196 34 477 A1.